D. Gavillet

PIREX II — A new irradiation facility for testing fusion first wall materials

Abstract A new irradiation facility, PIREX II (Proton Irradiation Experiment), became operational in March 1987. It is located on a dedicated beam line split from the main beam of the 590 MeV proton accelerator at the Paul Scherrer Institute (PSI). Irradiation with protons of this energy introduces simultaneously displacement damage, helium and other impurities. Because of the penetration range of 590 MeV protons, both damage and impurities are homogeneously distributed in the target material. The installation has its own beam line optics that can support a proton current of up to 50 μA. At a typical beam density of 4 μA mm 2 , the damage rate in steel is 0.7 × 10−5 dpa s (dpa: displacements per atom), and the helium production rat He/dpa. Both flat tensile specimens of up to 0.4 mm thickness and tubular fatigue samples of 3 mm diameter can be irradiated. Cooling of the sample is performed by flowing pressurized helium gas over the sample. Irradiation temperatures can be controlled between 100 ° C and 800 ° C. Installation of an in situ low cycle fatigue device is foreseen. Beams of up to 20 μA have been obtained, the beam having an approximately Gaussian distribution of elliptical cross section with 4σxbetween 0.8 and 8 nun by 4σy of up to 10 mm. Irradiations for a dosimetry program have been completed on samples of Al, Cu, Fe, Ni, Au, W, and 1.4914 ferritic steel. The evaluation of results allows the correct choice of reactions to be used for determining total dose, from the standpoint of half life and gamma energy. A program of irradiations on candidate materials for the Next European Torus (NET) design (Cu and Cu alloys, 1.4914 ferritic martensitic steel, W and W-Re alloys and Mo and Mo alloys), where the above mentioned characteristics of this type of irradiation can be used advantageously, is now under way.

The temperature dependence of the flow stress of 600-MEV proton irradiated aluminium

Abstract Tensile tests were performed on aluminium foils of 0.1 mm thickness that had been irradiated in the PIREX facility in the cyclotron of the Swiss Nuclear Research Institute (SIN) at doses between 0.9 to 5 dpa. Helium is produced at a measured rate of 230 appm/dpa simultaneously with the displacement damage. The post irradiation tests were performed in the range from 190 to 470 K. An increase of a factor four in the flow stress is found in the irradiated material at a dose 4.1 dpa at 190 K. The increase in flow stress is found to be proportional to the square root of the dose at all test temperatures. This increase has no clear correlation with bubble structure observed by TEM (either with bubble size or number density). These measurements, together with those of activation volume and TEM in-situ deformation, indicate that the main obstacle to dislocation glide is the presence of a dispersion of small ( ~ 1 nm diameter) clusters of impurities produced by spallation reactions during the irradiation. A modified Fleischer hardening model is used to describe the results. Good agreement with experimental data is found for a dislocation escape of 140°, which corresponds to the angle measured during the TEM in-situ deformations.

Effects of 600 MeV proton irradiation on nucleation and growth of precipitates and helium bubbles in a high-purity Al-Mg-Si alloy

Solution treated specimens of a high-purity Al-0.75%Mg-0.42%Si alloy were irradiated with 600 MeV protons at 150 and 240°C to a dose level of 0.47 and 0.55 dpa, respectively. Mg2Si-type precipitates formed during irradiation at 150 and 240°C; at 240°C, however, a large number of precipitates seem to have dissolved during the later stages of irradiation. Thermally aged reference specimens have also been investigated. The needle-shaped precipitates in the aged and the irradiated specimens lie along the 〈100〉 matrix directions. At 150°C bubbles were observed only at grain boundaries whereas at 240°C bubbles were seen in the grain interior as well as at the grain boundaries. Long rows of bubbles were observed with the same orientation in the matrix as the precipitate needles. Grain boundary bubbles were found to grow faster in the Al-Mg-Si alloy than in high-purity aluminium.

The microstructure of the 1.4914 MANET martensitic steel before and after irradiation with 590 MeV protons

Abstract Optical and transmission electron microscope observations, together with SEM (scanning electron microscope) and ASTEM (analytical scanning transmission electron microscope) microanalysis have been performed in samples of the DIN 1.4914 martensitic steel (MANET cast), both before and after irradiation with 590 MeV protons to doses up to 1 dpa at temperatures between 363 and 703 K. The chemical composition of the different carbide geometries have been obtained. No substantial modification of the carbide and precipitate structure is observed after either deformation under fatigue or after irradiation to 1 dpa at 703 K. No bubbles have been observed in a specimen irradiated to 0.7 dpa, containing 87 appm He.

Nucleation and growth of precipitates and helium bubbles in a high-purity AlMgSi alloy irradiated with 600 MeV protons

Abstract Irradiation-induced changes in the precipitation behaviour of age-hardening alloys are not yet well established. Very little is known about the problem of precipitation and precipitate stability particularly under fusion irradiation conditions leading to concurrent production of displacement damage and gaseous impurities at high rates. The main objective of the present work has been to study the effect of displacement damage, in the range from 0.01 to 1.63 dpa, with simultaneous production of helium atoms at a high rate ( ~ 214 appm/dpa) in a high purity Al-0.75% Mg-0.42% Si alloy; the composition is similar to that of the commercial type 6061 AlMgSi alloy. In order to study the effect of irradiation on the nucleation and growth of precipitates and the aggregation of concurrently produced helium atoms, the alloy was irradiated in the solution annealed condition (535°C, 35 min). The irradiation temperature varied between 120 and 260°C. After irradiation, the nucleation, growth and dissolution of Mg2Si-type precipitates as a function of irradiation dose and temperature were studied by transmission electron microscopy (TEM). The results show that the precipitation of Mg2Si-type particles occurs on a finer scale during irradiation than during thermal aging of the solution treated AlMgSi alloy (at the temperature of irradiation). The needle-shaped Mg2Si-type precipitates in the thermally aged and the irradiated specimens are found to lie along the 〈100〉 matrix directions. Information regarding nucleation and growth of helium bubbles in the matrix, at precipitate-matrix interfaces and at grain boundaries has also been obtained by TEM. Long rows of bubbles are found to be associated with the Mg2Si-type precipitates. The bubbles at the precipitate-matrix interfaces and at the grain boundaries are found to grow faster than those in the matrix. The implications of these results will be briefly discussed.